U.S. patent number 5,202,382 [Application Number 07/818,661] was granted by the patent office on 1993-04-13 for thermosetting powder coating composition containing a mixture of low tg and high tg polymers with acid functional groups.
This patent grant is currently assigned to PPG Industries, Inc.. Invention is credited to Paul H. Pettit, Jr..
United States Patent |
5,202,382 |
Pettit, Jr. |
April 13, 1993 |
Thermosetting powder coating composition containing a mixture of
low Tg and high Tg polymers with acid functional groups
Abstract
A thermosetting powder coating composition which has good
stability, pigment dispersion and impact characteristics is
disclosed. The composition comprises a co-reactable particle
mixture of an acid group-containing acrylic polymer having a Tg in
the range of -20.degree. C. to 30.degree. C., an acid
group-containing acrylic polymer having a Tg in the range of
40.degree. C. to 100.degree. C. and a curing agent, therefor.
Inventors: |
Pettit, Jr.; Paul H. (Wexford,
PA) |
Assignee: |
PPG Industries, Inc.
(Pittsburgh, PA)
|
Family
ID: |
27410777 |
Appl.
No.: |
07/818,661 |
Filed: |
January 9, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
590718 |
Oct 1, 1990 |
5098955 |
|
|
|
408856 |
Sep 18, 1989 |
4988767 |
|
|
|
Current U.S.
Class: |
525/108; 525/111;
525/131; 525/172; 525/176; 525/194; 525/214; 525/221; 525/934 |
Current CPC
Class: |
C09D
133/064 (20130101); C09D 133/064 (20130101); C09D
133/064 (20130101); C08L 33/064 (20130101); C08L
63/00 (20130101); C08L 2205/02 (20130101); C08L
2666/04 (20130101); C08L 2666/28 (20130101); C08L
2666/02 (20130101); Y10S 525/934 (20130101) |
Current International
Class: |
C09D
133/06 (20060101); C08L 33/06 (20060101); C08L
63/00 (20060101); C08L 33/00 (20060101); C08L
033/02 () |
Field of
Search: |
;525/108,194,214,221,934 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sellers; Robert E.
Attorney, Agent or Firm: Uhl; William J.
Parent Case Text
This is a division of application Ser. No. 07/590,718, filed Oct.
1, 1990, now U.S. Pat. No. 5,098,955, which is a division of
application Ser. No. 07/408,856, filed Sep. 18, 1989 now U.S. Pat.
No. 4,988,767.
Claims
What is claimed is:
1. A method for preparing a powder coating composition comprising
the steps of:
(a) preparing an acid group-containing polymer blend consisting of
(i) from about 1 percent to about 25 percent by weight based on the
weight of resin solids of a first acid group-containing acrylic
polymer having a Tg in the range of about -20.degree. C. to about
30.degree. C. and (ii) from about 40 percent to about 75 percent by
weight based on the weight of resin solids of a second acid
group-containing acrylic polymer having a Tg in the range of
40.degree. C. to about 100.degree. C.; and
(b) forming a co-reactable particulate mixture of the polymer blend
formed in step (a) and (iii) a polyepoxide curing agent capable of
reacting with acid groups in the polymer blend to form a
crosslinked product.
2. The method of claim 1 wherein step (a) is carried out by first
preparing the first acid group-containing acrylic polymer having a
Tg in the range of about -20.degree. C. to about 30.degree. C. and
then using said first acid group-containing polymer in solution as
a polymerization media for the preparation of the second acid
group-containing acrylic polymer having a Tg in the range of
40.degree. C. to about 100.degree. C.
3. The method of claim 1 wherein the acrylic polymers have a number
average molecular weight from about 1500 to about 15,000.
4. The method of claim 1 wherein the acrylic polymers are formed by
polymerizing an alpha, beta-ethylenically unsaturated carboxylic
acid selected from the group consisting of acrylic acid and
methacrylic acid, a C.sub.1 to C.sub.20 alkyl ester of acrylic or
methacrylic acid including mixtures of such esters and a
polymerizable vinyl aromatic compound.
5. The method of claim 4 wherein the acrylic polymers contain a
C.sub.1 to C.sub.2 alkyl ester of acrylic or methacrylic acid and a
C.sub.4 to C.sub.20 alkyl ester of acrylic or methacrylic acid.
6. The method of claim 1 wherein the polyepoxide is selected from
the group consisting of polyglycidyl ethers of aromatic polyols and
polyglycidyl ethers of polyhydric alcohols.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to thermosetting powder coating
compositions and more particularly to acrylic powder coating
compositions containing acid functionalized acrylics.
2. Brief Description of the Prior Art
Powder coating compositions for use in painting are extremely
desirable. Such coating compositions greatly reduce and can even
eliminate the organic solvents used in liquid paints. When the
powder coating composition is cured by heating, little, if any,
volatile material is given off to the surrounding environment. This
is a significant advantage over liquid paints in which organic
solvent is volatilized into the surrounding atmosphere when the
paint is cured by heating.
Carboxyl functional acrylic based powder coatings offer many
potential advantages relative to other types of powder coatings
including the capability of providing hard, chemically resistant
and exteriorly durable films. Additionally, when properly
formulated, these acrylic powder coatings can provide excellent
corrosion, stain and detergent resistance as well as forming
coatings which when exposed to high temperatures have good
non-yellowing characteristics. Examples of such powder coatings are
disclosed in U.S. Pat. No. 4,021,504 to Conrad and U.S. Pat. No.
4,727,111 to Pettit et al.
While acid functional acrylic based powders have many potential
advantages, they do suffer from some product limitations. The
inherently high viscosity of high Tg (>40.degree. C.) acid
functional acrylic resins makes them difficult to process in
typical powder extruders, resulting in poor mixing and relatively
poor flow and film smoothness. The high viscosity of the acrylic
resins, together with the poor mixing capability of such high Tg
materials, can give poor pigment dispersion during extrusion
processing, resulting in lower gloss coatings with less than
optimum hiding power. Finally, acrylic powders in general have poor
flexibility as evidenced by low impact and bend resistance.
Other thermosetting acid functional powder coatings such as
polyesters generally have somewhat better flexibility than
acrylics, but certain uses for these materials also require
improved impact and bend resistance.
SUMMARY OF THE INVENTION
The composition of the present invention comprises 1 to 20 percent
by weight of an acid group-containing polymer having a Tg from
-20.degree. C. to 30.degree. C., from 50 to 75 percent by weight of
a second acid group-containing polymer having a Tg in the range of
40.degree. C. to 100.degree. C. and a curing agent capable of
reacting with acid groups in the polymers to form a crosslinked
product. Such compositions have good processability, good powder
stability, i.e., do not clump when exposed to heat, and can give
coatings with good exterior durability and a good blend of other
physical properties such as good appearance, flexibility, hardness,
solvent resistance and corrosion resistance. They also have
improved pigment dispersions, i.e., higher gloss, less pigment
float and good impact, and adhesion characteristics.
DETAILED DESCRIPTION
When the acid group-containing polymers are acrylic polymers, both
the high and low Tg acid group-containing acrylic polymers
preferably have a number average molecular weight of about 1,500 to
15,000, preferably 2,300 to 6,000. The high Tg acrylic polymer has
a glass transition temperature (Tg) in the range of 40.degree. C.
to 100.degree. C. The low Tg acrylic polymer has a Tg in the range
of -20.degree. C. to 30.degree. C. The high Tg acrylic polymer
provides for hardness, gloss, durability and solvent resistance in
the resulting coating. The low Tg acrylic polymer contributes
flexibility and improved leveling, good pigment dispersion and
dispersion stability.
The molecular weights of the acrylic polymer are determined by gel
permeation chromatography (GPC) using a polystyrene standard.
Therefore, it is not the actual molecular weight which is measured
but an indication of the molecular weight as compared to
polystyrene. The values which are obtained are commonly referred to
as polystyrene numbers; however, for the purposes of this
application, they are referred to as molecular weights. If the
number average molecular weight is below 1500, the solvent
resistance and mechanical strength of the resultant coating may be
poor. If the molecular weight is higher than 15,000, the melt flow
of the polymer is low and the coating may have poor appearance.
The Tg of the polymer is a measure of the hardness and melt flow of
the polymer. The higher the Tg, the less the melt flow and the
harder the coating. Tg described in PRINCIPLES OF POLYMER CHEMISTRY
(1953), Cornell University Press. The Tg can be actually measured
or it can be calculated as described by Fox in Bull. Amer. Physics
Soc. 1, 3, page 123 (1956). Unless stated otherwise, Tg as used
herein refers to actually measured values. For measurement of the
Tg of the polymer, differential scanning calorimetry can be used
(rate of heating 10.degree. C. per minute, Tg taken at the first
inflection point).
If the glass transition temperature of the high Tg acrylic polymer
is below 40.degree. C., the powder tends to cake. If the glass
transition temperature of the high Tg acrylic polymer is above
100.degree. C., it will tend to be highly viscous and brittle. In
the case of the low Tg acrylic polymer, if the Tg is above
30.degree. C., there is no significant improvement. If the Tg is
below -20.degree. C., there is poor powder stability.
Carboxylic acid group-containing acrylic polymers can be formed by
reacting a polymerizable alpha, beta-ethylenically unsaturated
carboxylic acid with one or more polymerizable alpha,
beta-ethylenically unsaturated monomers, particularly vinyl
aromatic monomers and esters of alpha, beta-ethylenically
unsaturated carboxylic acids.
Examples of the carboxylic acid group-containing monomers which can
be used are acrylic acid and methacrylic acid, which are preferred,
as well as crotonic acid, itaconic acid, fumaric acid, maleic acid,
citraconic acid, and the like, as well as monoalkylesters of
unsaturated dicarboxylic acids. The acid group-containing monomer
is preferably present in the polymer in amounts of about 6 to 25
percent by weight, more preferably from 8 to 18 percent by weight
on total weight of the monomers. Amounts less than 6 percent by
weight may result in poor solvent resistance and poor mechanical
strength of the coating.
Examples of vinyl aromatic compounds are monofunctional vinyl
aromatic compounds such as styrene, which is preferred, and
alkyl-substituted styrenes such as alpha-methylstyrene and
chloro-substituted styrene such as chlorostyrene. For exteriorly
durable products, the vinyl aromatic monomer is preferably present
in the composition in amounts of about 5 to 45, more preferably
from 10 to 25 percent by weight based on the total weight of the
monomers. Amounts less than 5 percent by weight may result in poor
corrosion resistance, whereas amounts greater than 25 percent by
weight may result in poor exterior durability.
Examples of esters of alpha, beta-ethylenically unsaturated acids
are esters of acrylic and methacrylic acid and include methyl
methacrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl
acrylate, dodecyl acrylate, methyl methacrylate, ethyl
methacrylate, lauryl methacrylate, N-butyl methacrylate and
2-ethylhexyl methacrylate. Preferably, these esters are present in
amounts of about 5 to 80, more preferably from about 30 to 70
percent by weight based on total weight of the monomers.
Preferably, the esters of the alpha, beta-ethylenically unsaturated
acids are a mixture of C.sub.1 to C.sub.2 alkyl esters and C.sub.4
to C.sub.20 alkyl esters, such as a mixture of methyl methacrylate
and butyl acrylate. Preferably, the C.sub.4 to C.sub.20 alkyl ester
is present in amounts of 5 to 80, more preferably 10 to 60 percent
by weight based on total weight of monomers. For the high Tg
acrylic polymer, amounts less than 5 percent by weight may result
in coatings with poor flexibility and impact resistance, whereas
amounts greater than 30 percent by weight may cause stability
problems in the coating composition. For the low Tg acrylic
polymer, amounts less than 30 percent by weight would result in a
lack of flexibility and pigment dispersion while amounts more than
65-70 percent might cause stability problems. The C.sub.1 to
C.sub.2 alkyl ester is preferably present in amounts of 15 to 80,
more preferably present in amounts of 30 to 60 percent by weight
based on total weight of the monomers in the high Tg resin and 0 to
45 percent in the low Tg resin. Amounts less than 15 percent by
weight in the high Tg resin may result in coatings with poor
hardness and durability, whereas amounts greater than 80 percent by
weight may result in coatings with poor flexibility. If the low Tg
resins are more than 45 percent, stability problems might
result.
In addition to the vinyl aromatic compounds and esters of acrylic
and methacrylic acid, other ethylenically unsaturated
copolymerizable monomers may be used. Examples include nitriles
such as acrylonitrile, vinyl and vinylidene halides such as vinyl
chloride and vinylidene fluoride and vinyl esters such as vinyl
acetate. These additional monomers are present in amounts of about
0 to 40, preferably from 0 to 30 percent by weight based on total
weight of monomers.
In preparing the acid group-containing acrylic polymers, the
various monomers are mixed together and are reacted by conventional
free radical initiated polymerization processes. Among the free
radical initiators which may be used are benzoyl peroxide,
tertiarybutyl hydroperoxide, ditertiarybutyl peroxide,
azobis(2-methylpropionitrile) and so forth. Chain transfer agents
such as mercaptopropionic acid can also be used. The polymerization
is preferably carried out in solution using a solvent in which the
monomers are soluble such as toluene or xylene. At the completion
of the polymerization, the reaction mixture is devolatilized such
as by placing it under vacuum to remove the organic solvent and
recovering the polymer as a solid material. Alternately, the
polymer can be precipitated and subsequently dried. Usually, the
devolatilized polymer will contain less than 1 percent by weight of
materials that volatilize at the temperatures used for curing the
coatings.
The acid group-containing acrylic polymers can also be prepared by
emulsion polymerization, suspension polymerization, bulk
polymerization or suitable combinations thereof. These techniques
are well known in the art. Besides free radical initiated
polymerization, other means of polymerization such as group
transfer and anionic polymerization can be used to prepare the
acrylic polymers.
The low Tg acid group-containing acrylic polymer is preferably used
in amounts of about 1 to 25 percent, more preferably 10 to 20
percent by weight based on weight of resin solids. The high Tg acid
group-containing acrylic polymer is preferably used in amounts of
about 40 to 75 percent, more preferably 50 to 60 percent by weight
based on weight of resin solids. Amounts of more than 25 percent by
weight and less than 40 percent by weight, respectively, of the low
Tg acid group-conytaining acrylic polymer and the high Tg acid
group-containing acrylic polymer are not preferred because of
stability concerns. Amounts greater than 75 percent by weight of
the high Tg acid group-containing acrylic polymer may result in
coatings with poor flow, flexibility, and impact strength while
amounts less than 40 percent might result in stability
problems.
Besides the carboxylic acid group-containing materials described
above, other optional polycarboxylic acid group-containing
materials can be included in the composition. Examples of these
other materials are carboxylic acid group-containing polyesters and
carboxylic acid group-containing polyurethanes.
The carboxylic acid group-containing polyester contributes
flexibility, impact resistance and corrosion resistance to coatings
deposited from the compositions of the present invention. Among the
carboxylic acid group-containing polyesters which may be used are
those based on condensing aliphatic including cycloaliphatic
polyols with aliphatic and/or aromatic polycarboxylic acids and
anhydrides. Examples of suitable aliphatic polyols include ethylene
glycol, propylene glycol, butylene glycol, 1,6-hexylene glycol,
neopentyl glycol, cyclohexanedimethanol, trimethylolpropane and the
like. Suitable polycarboxylic acids and anhydrides include succinic
acid, adipic acid, azelaic acid, sebacic acid, terephthalic acid,
isophthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid,
trimellitic acid and anhydrides of such acids.
These ingredients are reacted together with an excess of acid to
alcohol so as to form a polyester which has free carboxylic acid
groups. Preferably, on a resin solids basis, the carboxylic acid
group-containing polyester will have an acid number of about 15 to
300 and will be a solid at room temperature. If the polyester is
present in the composition, it is present in amounts of 5 to 40
percent by weight, preferably about 15 to 35 percent by weight
based on weight of resin solids. Amounts greater than 40 percent by
weight are undesirable because of tendencies towards poor solvent
resistance and poor exterior durability in the coating.
The carboxylic acid group-containing polyurethane contributes
durability to the resultant coating. The polyurethane can be
prepared by reacting polyols and polyisocyanates so as to form a
polyurethane polyol which is then reacted with polycarboxylic acid
or anhydride to introduce free carboxyl groups into the reaction
product. Examples of polyols include those mentioned above in
connection with the preparation of the polyester. Examples of
polyisocyanates are aromatic and aliphatic polyisocyanates with the
aliphatic polyisocyanates being preferred because of better
exterior durability. Specific examples include 1,6-hexamethylene
diisocyanate, isophorone diisocyanate and
4,4'-methylene-bis-(cyclohexyl isocyanate). Examples of suitable
polycarboxylic acids are those mentioned above in connection with
the preparation of the polyester. Preferably, the carboxylic acid
group-containing polyurethane has an acid number on a resin solids
basis of about 15 to 300 and will be a solid at room temperature.
If the polyurethane is used, it is used in amounts of 5 to 40
percent by weight, preferably about 15 to 35 percent by weight
based on weight of resin solids. Amounts greater than 40 percent by
weight are undesirable because of poor stability in the coating
composition.
Curing agents are those materials capable of reacting with acid
groups to form a crosslinked product. Of most significance are
polyepoxies and beta-hydroxyalkylamides.
A wide variety of polyepoxides may be utilized as in the powder
coating compositions. Preferably, the polyepoxide should have a
1,2-epoxy equivalency greater than one and more preferably greater
than about 1.9. Examples of useful polyepoxides are polyglycidyl
ethers of aromatic polyols, e.g., polyphenols. Such polyepoxides
can be produced, for example, by etherification of an aromatic
polyol with epichlorohydrin or dichlorohydrin in the presence of an
alkali. The aromatic polyol may be, e.g.,
bis(4-hydroxyphenyl)-2,2-propane (generally known as bisphenol A),
bis(4-hydroxyphenyl)-1,1-ethane,
bis(4-hydroxyphenyl)-1,1-isobutane, bis(4-hydroxy
tertiarybutylphenyl)-2-2-propane, bis(2-hydroxynaphthyl)methane,
4,4'-dihydroxybenzophenone, 1,5-dihydroxynaphthalene and the like.
Polyepoxides based on bisphenol A are preferred from among the
polyglycidyl ethers of aromatic polyols.
Also, suitable as the polyepoxide are polyglycidyl ethers of
polyhydric alcohols, such as 1,2-ethanediol, 1,2-propanediol,
1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, diethylene
glycol, triethylene glycol, polyethylene glycol, polypropylene
glycol and the like. Also suitable would be cycloaliphatic epoxies
such as ERL-4221 available from Union Carbide Corporation and
EHPE-3150 available from Daicel.
Generally, the polyepoxides have epoxy equivalent weights from
about 100 to 1,000, preferably from about 150 to about 800. The
polyepoxides are preferably present in amounts from about 2 to
about 45 percent by weight, more preferably from about 10 to about
40 percent by weight based on total weight of resin solids in the
powder coating composition.
The beta-hydroxyalkylamide curing agents can be depicted
structurally as follows: ##STR1## where R.sub.1 is H or C.sub.1
-C.sub.5 alkyl; ##STR2## or wherein R.sub.1 is as described above;
A is a bond, monovalent or polyvalent organic radical derived from
a saturated, unsaturated or aromatic hydrocarbon including
substituted hydrocarbon radicals containing from 2 to 20 carbon
atoms. Preferably, A is an alkylene radical --(CH.sub.2)X-- where X
is equal to 0 to 12, preferably 4 to 10; m is equal to 1 to 2 and n
is equal to 0 to 2 and m+n is at least 2, preferably greater than
2, usually within the range of being greater than 2 and up to and
including 4.
The beta-hydroxyalkylamides can be prepared by reacting a lower
alkyl ester or mixture of esters of carboxylic acids with a
beta-hydroxyalkylamine at a temperature ranging from ambient
temperature up to about 200.degree. C., depending on the choice of
reactants and the presence or absence of catalyst. Suitable
catalysts includes sodium and potassium methoxide or butoxide
present in amounts of about 0.1 to 1 percent by weight based on
weight of alkyl ester.
To bring about effective cure of the composition, the equivalent
ratio of acid to the curing group, i.e., epoxy group or
beta-hydroxyalkylamide group, is from about 1.6/1.0 to 0.5/1.0,
more preferably in the range of 1.3/1.0 to 0.7/1.0. Ratios outside
these ranges are undesirable because of poor cure.
In order to give the powder coating composition a suitable color, a
pigment can be included in the coating composition typically in
amounts of from about 1 to 50 percent by weight based on total
weight of the powder coating composition. Pigments which are
suitable for powder coating compositions include basic lead silica
chromate, titanium dioxide, ultramarine blue, phthalocyanine blue,
phthalocyanine green, carbon black, black iron oxide, chromium
green oxide, ferrite yellow and quindo red.
The coating composition may also contain certain other additives
that are typically incorporated into powder coating compositions
such as degassing agents, flow control agents, UV absorbing agents,
and anti-oxidants.
Particularly recommended are degassing agents which allow volatiles
to escape from the film during baking and flow control agents which
prevent cratering of the finish. Benzoin is a highly preferred
degassing agent and when used is present in amounts ranging from
0.5 to 3 percent by weight based on total weight of the
composition.
One group of suitable flow control agents are acrylic polymers such
as polylauryl acrylate, polybutyl acrylate, poly(2-ethylhexyl)
acrylate, poly(ethyl-2-ethylhexyl) acrylate, polylauryl
methacrylate and polyisodecenyl methacrylate. The flow control
agent may also be a fluorinated polymer such as an ester of
polyethylene glycol or polypropylene glycol and fluorinated fatty
acids, for example, an ester of polyethylene glycol of a molecular
weight of over 2500 and perfluorooctanoic acid. Polymeric siloxanes
of molecular weights over 1000 may also be used as a flow control
agent, for example, poly(dimethylsiloxane) or
poly(methylphenyl)siloxane. The flow control agent when used is
present in amounts of about 0.5 to 5 percent by weight based on
total weight of the coating composition.
For good exterior durability, the compositions also preferably
contain UV absorbing agents and anti-oxidants. Such materials are
commerically available from Ciba-Geigy under the trademark TINUVIN
and IRGANOX. The UV absorbing agents and anti-oxidants when used
are typically present in the compositions individually in amounts
of about 1.5 to 6 percent by weight based on weight of resin
solids.
The thermosetting powder coating compositions are prepared by melt
blending the ingredients of the coating compositions. This can be
accomplished by first blending in a high-intensity mixer and then
melt blending in an extruder at a temperature of about 80.degree.
to 130.degree. C. The extrudate is then cooled and particulated
into a powder. The powder coating composition can then be applied
directly to metal such as steel or aluminum, glass, plastic or
fiber-reinforced plastic substrates.
As an alternative to producing two separate acrylic polymers, a
high Tg and low Tg, it would also be possible to prepare an acid
group-containing polymer blend consisting of (i) from about 1
percent to about 25 percent by weight based on the weight of resin
solids of monomers from which a first acid group-containing polymer
having a Tg in the range of about -20.degree. C. to about
30.degree. C. might be prepared and (ii) from about 40 percent to
about 75 percent by weight based on the weight of resin solids of
monomers from which a second acid group-containing polymer having a
Tg in the range of 40.degree. C. to about 100.degree. C. might be
prepared. A co-reactable particulate mixture of the polymer blend
and a curing agent capable of reacting with acid groups in the
polymer blend to form a crosslinked product may then be formed. The
blend may be prepared by first preparing the first acid
group-containing polymer having a Tg in the range of about
-20.degree. C. to about 30.degree. C. and then using said first
acid group-containing polymer in solution as a polymerization media
for the preparation of the second acid group-containing polymer
having a Tg in the range of 40.degree. C. to about 100.degree. C.
The polymers may be acrylic polymers of any of the types disclosed
above. The curing agent may also be either a beta-hydroxyalkylamide
or a polyepoxide of any of the types disclosed above.
Application of the powder can be by electrostatic spraying or by
the use of a fluidized bed. Preferred is electrostatic spraying,
the powder composition can be applied in one pass or in several
passes to provide a film thickness after cure of about 0.5 to 5
mils. Preferably, to provide a high-quality finish at reasonable
cost, the thickness of the powder coat is about 1.2 to 4 mils,
preferably 1.4 to 3 mils.
The substrate to be coated can optionally be preheated prior to
application of the powder to promote more uniform powder
deposition. Upon application of the powder, the powder-coated
substrate is baked typically at 250.degree. to 400.degree. F.
(121.degree. to 204.degree. C.) for about 20 to 60 minutes.
The present invention will be more fully understood from the
following illustrative examples wherein all quantities, percentages
and ratios are on a weight basis unless otherwise indicated.
The following examples (A-E) show the preparation of various
carboxylic acid group-containing polymers.
EXAMPLE A
A high Tg carboxylic acid group-containing acrylic polymer was
prepared from the following ingredients:
______________________________________ Ingredients Parts by Weight
(grams) ______________________________________ Reactor Charge
Xylene 2400 Initiator Charge LUPERSOL 555-M60.sup.1 350 Xylene 795
Monomer Charge Styrene 900 (15%) Methyl methacrylate 3750 (62.5%)
Butyl acrylate 720 (12.0%) Acrylic acid 630 (10.5%) Rinse/Post Add
Xylene 336 Liquid MODAFLOW.sup.2 18.0
______________________________________ .sup.1 LUPERSOL 555M60 is an
amyl peroxide catalyst available from Lubrizol Corp. .sup.2 Liquid
MODAFLOW is poly(2ethylhexyl-ethyl) acrylate available from
Monsanto Co.
The reaction charge was heated under a nitrogen atmosphere to
reflux. The initiator charge and monomer charge were then added
slowly and simultaneously to the reactor charge over a period of
three hours while keeping the reaction mixture at reflux. After the
feeds of the initiator charge and monomer charge were completed,
the reaction mixture was held for 2 hours at reflux, and then the
post-add rinse was added. The reaction mixture was then heated
under vacuum to remove solvent. The resultant reaction product had
a solids content of 99.7 percent, an acid value of 77, a number
average molecular weight of 3500 and a measured Tg of 64.degree. C.
Molecular weights were determined by gel permeation chromatography
using a polystyrene standard, and Tg was measured using a DU PONT
Model #2100 Thermal Analyzer.
EXAMPLE B
A low Tg carboxylic acid group-containing acrylic polymer was
prepared from the following ingredients:
______________________________________ Ingredients Parts by Weight
(grams) ______________________________________ Reactor Charge
Xylene 2400 Initiator Charge LUPERSOL 555-M60 350 Xylene 795
Monomer Charge I Styrene 450 Methyl methacrylate 1110 Butyl
acrylate 1462 Acrylic acid 220.5 Monomer Charge II (cumulative)
Styrene 450 (15%) Methyl methacrylate 1110 (37%) Butyl acrylate
787.5 (37.5%) Acrylic acid 409.5 (10.5%) Rinse/Post Add Xylene 336
Liquid MODAFLOW 18.0 ______________________________________
The polymer was prepared as generally described above in Example A
except that monomer charge I was added first over a period of 1.5
hours, followed by monomer charge II added over a period of 1.5
hours. The polymer after stripping had a solids content of 99.7
percent, an acid value of 76.1, a number average molecular weight
of 3500 and a measured Tg of 27.degree. C.
EXAMPLE C
To eliminate the need to produce two separate acrylic polymers, a
high Tg and low Tg, a modified process was used in which the low Tg
acrylic was prepared and the solution of the low Tg acrylic used as
the polymerization media for the high Tg acrylic. The carboxylic
acid group-containing acrylic polymer was prepared from the
following ingredients:
______________________________________ Ingredients Parts by Weight
(grams) ______________________________________ Reactor Charge
Xylene 800 Liquid MODAFLOW 6 Initiator Charge I LUPERSOL 555-M60 16
Xylene 60 Monomer Charge I Lauryl methacrylate 128 Butyl
methacrylate 244 Acrylic acid 28 Mercaptopropionic acid 6.4
Initiator Charge II LUPERSOL 555-M60 64 Xylene 241.6 Monomer Charge
II Styrene 256 Methyl methacrylate 960 Butyl methacrylate 240
Acrylic acid 136.8 Mercaptopropionic acid 25.6 Monomer Charge III
Acrylic acid 7.2 Xylene 30 Rinse Xylene 100
______________________________________
The polymerization was conducted as generally described in Example
A except that monomer and initiator charge I was added over one
hour with a ten minute hold prior to start of initiator II and
monomer II charges. Monomer and initiator charges II were added
over a 90-minute period and then monomer charge III added over a
30-minute period. The reaction mixture was held at reflux for 90
minutes. The reaction mixture was then heated under vacuum to
remove solvent. The resultant reaction product had a solids content
of 99.7 percent, an acid value of 69.5 and a number average
molecular weight of 3000. Calculated Tg of the low Tg acrylic was
approximately 0.degree. C.
EXAMPLE D
A high Tg carboxylic acid group-containing acrylic polymer was
prepared from the following ingredients:
______________________________________ Ingredients Parts by Weight
(grams) ______________________________________ Reactor Charge
Xylene 800 Liquid MODAFLOW 6.0 Initiator Charge LUPERSOL 555-M60
83.3 Xylene 298.7 Monomer Charge Styrene 1000 (50%) Butyl
methacrylate 780 (39%) Acrylic acid 209 (11%) Mercaptopropionic
acid 32 (chain transfer) Rinse Xylene 100
______________________________________
The polymer was prepared as described above in Example A. The
polymer after stripping has a solids content of 99.7 percent, an
acid value of 88, a number average molecular weight of 3200 and a
calculated Tg of 70.degree. C. Melt viscosity measured at
180.degree. C. using a BROOKFIELD Thermal Cell Viscometer at 2.5
ppm was 8360 cps.
EXAMPLE E
A 75/25 blend of the same high Tg polymer described in Example D
with a low Tg acrylic was prepared using the process described in
Example C. The carboxylic acid group-containing acrylic polymer was
prepared from the following ingredients:
______________________________________ Ingredients Parts by Weight
(grams) ______________________________________ Reactor Charge
Xylene 800 Liquid MODAFLOW 6 Initiator Charge I LUPERSOL 555-M60
12.5 Xylene 83.0 Monomer Charge I Styrene 75 (15%) Butyl acrylate
250 (50%) Butyl methacrylate 135 (27%) Acrylic acid 40 (8%)
Mercaptopropionic acid 8 (chain transfer) Initiator Charge II
LUPERSOL 555-M60 57.5 Xylene 229 Monomer Charge II Styrene 750
(50%) Butyl methacrylate 585 (39%) Acrylic acid 165 (11%)
Mercaptopropionic acid 24 (chain transfer) Rinse Xylene 100
______________________________________
The polymer was prepared as described in Example C above. After
stripping, the polymer has a solids content of 99.7 percent, an
acid value of 85, and a number average molecular weight of 3500.
Calculated Tg of the high Tg component is 70.degree. C. and the
calculated Tg of the low Tg polymer is about 2.degree. C. Melt
viscosity measured at 180.degree. C. using a BROOKFIELD Thermal
Cell Viscometer at 2.5 ppm was 1440 cps.
EXAMPLE F
An acid functional polyester was prepared from the following
ingredients:
______________________________________ Ingredients Parts by Weight
(grams) ______________________________________ 1,6-hexanediol 118
Dodecanedioic acid 460 Dibutyltin oxide 0.58 Xylene 144.6
______________________________________
The ingredients were charged to a reactor and heated under a
nitrogen atmosphere to reflux (about 140.degree. C.). The reaction
mixture was gradually heated to about 165.degree. C. while
azeotropically distilling water until an acid value of 163 was
obtained. The reaction mixture was then heated at 125.degree. C.
under vacuum to remove solvent and then cooled to room temperature
to give a solid reaction product which had a solids content of 100
percent (two hours at 140.degree. C.), an acid value of 208, a
melting point range of 95.degree. C. to 105.degree. C. and a number
average molecular weight of 952.
EXAMPLE G
Bis[N,N-di(beta-hydroxyethyl)]adipamide-glutaramide was prepared
from the following mixture of ingredients:
______________________________________ Ingredients Parts by Weight
(grams) ______________________________________ 90/10 weight ratio
of 1038.0 dimethyladipate/dimethyl glutarate Diethanolamine 1512.0
Methanolic sodium methoxide 4.7 (20 ml)
______________________________________
The ingredients were charged to a reaction vessel and heated to
about 100.degree. C. at which point the distillation of methanol
began. Reaction was continued while distilling methanol (303 grams)
until a temperature of 128.degree. C. was reached. An additional 5
ml of methanolic sodium methoxide was added and heating continued
until an additional 5 grams of methanol was obtained. A slight
vacuum was applied to the reaction flask and an additional 28 grams
of methanol was removed. The methanol distillate was added slowly
back into the reaction mixture followed by the addition of 2000 ml
of acetone. As the reaction mixture cooled, the hydroxyalkylamide
precipitated. The precipitate was filtered, washed with acetone and
air dried to yield a reaction product melting at
114.degree.-118.degree. C.
EXAMPLES 1-4
Powder coating compositions were prepared from the mixtures of
ingredients as shown on Table I below. The polymers were blended
with the other ingredients in the formulation in a HENSCHEL mixer
and then melt blended in a BAKER PERKINS twin screw extruder at
130.degree. C. The extrudate was chilled and flaked on a chill roll
at 40.degree. C., ground in a micromill and sieved through a 140
mesh screen. The resulting powder was then electrostatically
sprayed onto grounded zinc phosphate pretreated steel panels using
an electrostatic spray gun. The coated panels were then baked at
177.degree. C. to form hard glossy coatings. The properties of the
resultant coating as well as the stability of the coating
composition are reported in Table II below.
TABLE I ______________________________________ Example 1 2 3 4
Ingredient (Parts by Weight) ______________________________________
Carboxylic acid group-containing 51 57 63.9 71.2 polymer of Example
A Carboxylic acid group-containing 20.2 14.2 7.3 0 polymer of
Example B Polyester flexibilizer 12.7 12.7 12.7 12.7 of Example F
Beta-hydroxyalkylamide of 16 16 16 16 Example G
______________________________________
TABLE II
__________________________________________________________________________
Impact Resistance.sup.3 Impact Resistance.sup.4 inch-pounds
(coating inch-pounds (coating Gloss.sup.2 thickness in mils)
thickness in mils) Example No. Stability.sup.1 20.degree.
60.degree. Direct Reverse Direct Reverse
__________________________________________________________________________
1 fair 91 79 160 160 140 160 2 good 90 79 160 140 100 140 3
excellent 90 78 160 140 100 120 4 excellent 90 75 90 100 80 60
__________________________________________________________________________
.sup.1 Stability determined by placing a sample of the powder
coating in 2 oz. glass jar and immersing in a water bath at
70.degree. C. for 3 days If there was clumping, a fair rating was
given. If there was slight clumping, a good rating was given. If
there was very slight clumping, an excellent rating was given.
.sup.2 The 20.degree. and 60.degree. gloss were measured with gloss
meter manufactured by the Gardner Instrument Company. .sup.3 The
impact resistance was measured with a GARDNER Impact Tester. The
coated panels were subjected to increasing amounts of impact unit
the coating cracked. The panel was impacted on the coating side,
i.e., direct impact, and also on the side of the coated panel
opposite the coating, i.e., reverse impact. The results are
reported in inchpounds and the thickness of the coating in mils is
shown in the parenthesis. Zinc phosphate pretreated steel panels
were used. .sup.4 Same as 3 except with iron phosphate pretreated
steel panels.
EXAMPLES 5-6
Powder coating compositions were prepared from the mixtures of
igredients as shown in Table III below. The polymers were blended
with the other ingredients in a HENSCHEL mixer and then melt
blended in a BAKER PERKINS twin screw extruder at 100.degree. C.
The extrudite was chilled and flaked on a chill roll at 40.degree.
C., ground in a micromill and sieved through a 140 mesh screen. The
resulting powder was then electrostatically sprayed onto grounded
steel panels using an electrostatic spray gun. The coated panels
were then baked at 177.degree. C. to form hard glossy coatings. The
properties of the resultant coatings are reported in Table IV
below.
TABLE III ______________________________________ Examples 5 6
Ingredient (Parts by Weight) ______________________________________
Carboxylic acid group-containing 500 polymer of Example D
Carboxylic acid group-containing 500 polymer of Example E EPON
828.sup.1 40 40 ECN-1299.sup.2 50 50 GT-9013.sup.3 100 100 Ethyl
triphenyl phosphonium acetate 3.0 3.0 catalyst (60% active on
silica) Black pigment 0.2 0.2 Blue pigment 1.0 1.0 Benzoin 4.8 4.8
MODAFLOW III.sup.4 5.0 5.0 IRGANOX 1076.sup.5 10 10
______________________________________ .sup.1 EPON 828 is a
bisphenol A epoxy resin available from Shell Chemica Co. .sup.2
ECN1299 is an epoxy cresole novolak available from CibaGeigy.
.sup.3 GT9013 is a bisphenol A epoxy available from CibaGeigy.
.sup.4 MODAFLOW III is poly(2ethylhexyl-ethyl) acrylate on silica
carrier available from Monsanto Co. .sup.5 IRGANOX 1076 is a
polyphenol stabilizer that inhibits oxidation available from
CibaGeigy.
TABLE IV ______________________________________ Ex- Impact
Resistance.sup.3 am- inch-pounds (coating ple Gloss.sup.2 thickness
in mils) No. Stability.sup.1 20.degree. 60.degree. Direct Reverse
Mandrel Bend.sup.4 ______________________________________ 5 fair 71
90 35 <5 Delamination 6 fair 89 95 70 15 No cracking
______________________________________ .sup.1 See footnote 1, Table
II. .sup.2 See footnote 2, Table II. .sup.3 See footnote 3, Table
II. .sup.4 The mandrel bend test is determined by bending coated
panels (4" .times. 12") around a 1/8 inch mandrel and measuring
cracking/delaminatio in inches along the bend line.
As can be seen from Tables II and IV, use of the blend of low Tg
and high Tg acrylic has significant effects on overall appearance
(gloss) as well as resulting in flexibility, processability and
pigment dispersion.
* * * * *